湖南花垣中寒武世晚期至晚寒武世早期球接子类

LATE MIDDLE AND EARLY LATE CAMBRIAN AGNOSTIDS IN HUAYUAN, HUNAN

在考察、实测了湘西地区数条剖面后,主要研究了花垣排碧剖面。建立了中寒武统上部至上寒武统下部的球接子类三叶虫带,这在湘西黔东地区尚属首次,为本区与国内、外有关地区的地层对比,提供了直接证据。本文详细讨论了这些对比证据,并系统描述了球接子类三叶虫新种和属于我国首次报道的种。此外,基于微相分析,概述了排碧地区中寒武世晚期至晚寒武世早期的沉积环境。

The section studied in the paper is situated in Paibi Village, Huayuan County, western Hunan (Text-fig. 1), containing a continuous sequence from the upper Lower Cambrian through the Upper Cambrian. This paper focuses on the strata from the upper Middle Cambrian through lower Upper Cambrian, which consist of unitary carbonate of deeper water, with a rich and diversified fauna of trilobites and conodonts. Through detailed sampling from the bottom of the Huaqiao Formation to the base of the Bitiao Formation, 93 trilobite-bearing horizons have been found, including 72 agnostid-bearing hortzons, with the erection of the Middle-Upper Cambrian trilobite (agnostid) zones which are recognized in descending order as follows: Upper Cambrian Series: Bitiao Formation (the lowermost part) 6. Glyptagnostus reticulatus Zone Chefu Formation 5. Glyptagnostus stolidotus Zone 4. Ammagnostus integriceps-Chatiania Zone Middle Cambrian Series: Huaqiao Formation 3. Lejopyge armata Zone Upper Part: Lejopyge laevigata and L. sinensis associated with the nominate zonal species L. armata. Lower Parts: Lejopyge laevigata and L sinensis absent. 2. Pseudophalacroma triangularis Zone 1. Ptychagnostus atavus Zone These zones can be correlated with those of related regions both at home and abroad (See Tables Ⅰ—Ⅱ), with the correlation explained in detail in this paper. Descriptions of new species Peratagnostus exilis sp. nov. (Pl. Ⅱ, fig. 8) Cephalon elliptical, a little wider than long, strongly convex, with no border. Dorsal furrow only seen in the basal part. A trace of basal lobes visible in some specimens. Pygidium subquadrate, a little wider than long, strongly convex. Axis faintly visible only in the anterior part, with an elongate median nodule on it. Border widening gradually and narrow posteriorly; marginal furrow narrow and clear. Remarks: The new species is distinguished from Peratagnostus sinus (Hsiang) (Xiang Liwen et al., 1985, p. 70, pl. 14, figs. 1—4) by the outlines of cephalon and pygidium and the narrow marginal furrow of pygidium. Occurrence: Lejopyge armata Zone, Huaqiao Formation, Huayuan, Hunan. Linguagnostus paibiensis sp. nov. (Pl. Ⅲ. figs. 3, 6) Cephalon subrotund, nearly as long as wide. Glabella subcylindrical, about three quarters as long as, and one-third as wide as cephalon. Transglabellar furrow curved posteriorly. Anterior glabellar lobe semicircular and short. Posterior lobe long, parallel-sided by deep dorsal furrow, with a faint elongate median node on its anterior hail. Cheeks separated anteriorly by longitudinal shal low depression instead of by preglabellar furrow. Basal lobes large and triangular. Marginal furrow broad and flat. Border narrow and convex. Pygidium subelliptical, wider than long. Axis short and relatively narrow, about half as long as and one-third as wide as pygidium, slightly narrowing posteriorly and divided into three lobes, with the second lobe longer than the others. A long median node running through anterior lobe, second lobe and anterior part of the third lobe. Depression behind the node wide and deep. A pair of furrows behind the depression extending posterolaterally, dividing the third lobe into three parts, i. e. a pair of subtrapezoidal lateral lobes and a lenticular posterior lobe. Transverse furrows faint, separated by the three axial lobes and by the long median node. Pleural lobes highly convex, connected with lateral marginal furrows by gentle slopes. Lateral marginal furrows extremely shallow and wide. Lateral border relatively wide and flat. A sinuous crest margining the posterior side of pleural lobes. Lateral parts of crest connected with posterior border by steep slopes, while middle part connected with posterior border by a nearly vertical slope, resulting in the absence of posterior marginal furrow. Posterior border wider, flatter and sinuous, parallel to crest. A median notch present at the centre of posterior border. Marginal spines small. Remarks: Based on its features and occurrence, the new species may be an intermediate type between Linguagnostus kjerulti (Brogger) and Cristagnostus paplio Rushton. Occurrence: Near the top of the Lejopyge armata Zone, Huaqiao Formation, Huayuan, Hunan.